The influence of diesel contaminated soil on Miscanthus x giganteus biomass thermal utilization and pyrolysis products composition

Abstract

The second-generation energy crop Miscanthus x giganteus (Mxg) demonstrated ability to produce adequate biomass yield even in marginal or contaminated soils. This renewable biomass can be utilized energetically or transformed into various biobased products and thus contribute to decrease of primary resources and fossil fuel use. To evaluate potential effects on energetic biomass properties Mxg was grown in diesel contaminated soils. Traces of total petroleum hydrocarbons were found solely in the leaves, however most likely resulting from air contamination. No differences were detected in the elemental composition of the raw biomass. Biomass combustion heat value reached average of 17.23 ± 0.21 MJ kg−1; contamination-originated leaves had slightly but significantly decreased heat values (14.41 ± 1.10 MJ kg−1) while heat of other parts was comparable to control. Thermogravimetric curves, simulating thermic utilization processes, were comparable both under oxygen (combustion) and nitrogen (pyrolysis). No diesel impacts were observed on the pyrolysis products yield. Higher amounts of CH4, C2H6, C3H4, C3H6 and C3H8 were detected in the pyrolysis gas from aboveground biomass from contaminated soil. Diesel contamination decreased significantly biochar surface. Concentrations of acids and esters in biooil were increased on the expense of concentrations of furans in the case of samples from contaminated soils. No significant effect on phenols and ketones concentrations in the biooil was observed. The amount of acetic acid, as the main biooil component, increased in the above- and below-ground plant parts along with the higher diesel concentrations in soil. Despite slight changes detected, the parameters of the biomass produced in diesel-contaminated soils present no obstacle to its energetic utilization and Mxg can be recommended for productive phytomanagement of such soils.